package com.company;

import java.util.Scanner;

public class Main31 {
    public static void main(String[] args) {
        double x1,x2,y1,y2;
        Scanner sr =new Scanner(System.in);
        x1= sr.nextInt();
        y1= sr.nextInt();
        x2= sr.nextInt();
        y2= sr.nextInt();
        double v=Math.sqrt(((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2)));
         v=(double) Math.round(v* 100) / 100;
        System.out.println(v);
    }

}
